Update index.md

Lezione 2013-04-05 sistemata con integrazione di appunti
index.md: revert part of @PeppeRp patch

Namely, revert the part that disposed of the work I did while he
was editing the patch.

I'm quite sure this wasn't the fault of @PeppeRp, but rather what
happens when you edit concurrently with GitHub's web interface.
index.md: wrap long lines
Merge branch 'PeppeRp-patch-1'